Feeds contain proteins, carbohydrates, fats, minerals, and vitamins. In general, defatted soybeans, fish meal, meat bone meal, rapeseed cake and the like are employed as the protein sources; corn, wheat flour and the like as the carbohydrate sources; animal and vegetable fats as fat sources. Among mineral sources, calcium carbonate, calcium phosphate, pulverized shell and the like are employed as the calcium sources; and ferric chloride, ferrous sulfate and the like as the iron sources.
Large energy intake for promotion of livestock and poultry growth tends to result in increased body fat content in their animals. However, because people have become more health consicious and try to reduce intake of animal fat, it is widely demanded to develop a breeding method or a feed to produce animals with less body fat.
As examples of feed for livestock and poultry which makes body fat content reduced, Japanese Patent Unexamined Publication No. HEI 03-219838 discloses that valine, leucine and isoleucine as amino acid components are blended into a feed at 0.01.about.3.00% by weight, respectively. And, Japanese Patent Publication No. HEI 06-95892 discloses that vitamin D.sub.3 is blended or mixed into a feed at 750.about.2500 .mu.g per kg of feed.
There is poly-.gamma.-glutamic acid, the main component of a viscous substance of femented soybeans called natto in Japan, as a substance which is capable of solubilizing minerals in the intestinal tract and which accelerates absorption of minerals. Poly-.gamma.-glutamic acid has an ability to solubilize minerals owing to its many carboxyl groups present in the molecules. Furthermore, poly-.gamma.-glutamic acid is considered to maintain its activity even in the intestinal tract because it is combined with .gamma.-peptide bond which remains unhydrolyzed with digestive enzymes present in the small intestine. Foods and beverages containing poly-.gamma.-glutamic acid are known (Japanese Patent Unexamined Publication Nos. HEI 03-30648 and HEI 05-316999). While any feed for reducing body fat which contains poly-.gamma.-glutamic acid has not been known yet.
An object of the present invention is to develop a feed composition which can reduce the amount of body fat in livestock and poultry, especially abdominal fat.